Unknown and short-lived MOS6522 Revision 1 (vs. Rev. 0)
Posted: Wed May 17, 2023 9:57 am
Some time ago someone pointed out that (contrary to my belief that there's only one revision of the VIA / 6522 (i.e. Rev. 0))
MOS also produced a 2nd version "R1" for a short period of time (around 1988) but resumed using the Rev. 0 layout:
One can distinguish the revision by looking at the second number (if present) on the MOS/CSG chips. For the 6522
it's either "10" (== Rev.0) or "11" (== Rev.1). This version can be found in 1541-II drives by example.
As the 6522 is plagued by the infamous shift-register bug we speculated if MOS/CSG fixed the bug but
withdrew that revision because of other incompatibilities or if it's even just a misprint!?
In order to find out finally I had to take a look at the silicon:
-
The result is that CSG just added a "(M) 1986 CBM" marker in the top left corner of the die AND
added a different (better?) ESD protection to the pins. The shift register control etc. doesn't seem to be different
at all (at least on the metal layer which I compared).
One can take a look at the bonding pad for the RESET# pin to get an idea of the change:
R0 v. R1:
-
MOS also produced a 2nd version "R1" for a short period of time (around 1988) but resumed using the Rev. 0 layout:
it's either "10" (== Rev.0) or "11" (== Rev.1). This version can be found in 1541-II drives by example.
As the 6522 is plagued by the infamous shift-register bug we speculated if MOS/CSG fixed the bug but
withdrew that revision because of other incompatibilities or if it's even just a misprint!?
In order to find out finally I had to take a look at the silicon:
added a different (better?) ESD protection to the pins. The shift register control etc. doesn't seem to be different
at all (at least on the metal layer which I compared).
One can take a look at the bonding pad for the RESET# pin to get an idea of the change:
R0 v. R1:
